1. Field of the Invention
The present invention relates to an apparatus for controlling an internal combustion engine, and more specifically, relates to a control apparatus for controlling a heater of an exhaust gas sensor of an internal combustion engine mounted in a vehicle. Moreover, the control apparatus according to an embodiment of the present invention is favorably used in the case of a mode in which changeover between an operating state and a shutdown state of the internal combustion engine is performed repeatedly during driving of the vehicle, and the shutdown state of the internal combustion engine continues for a relatively long time.
2. Description of Related Art
Recently, in order to enhance fuel efficiency in vehicles, a hybrid vehicle has been proposed as an electric vehicle and has been put into practical use.
The hybrid vehicles may be classified into a series hybrid vehicle in which electric energy is generated by driving a generator by an internal combustion engine and a motor drives the vehicle by the electric energy, and a parallel hybrid vehicle in which an internal combustion engine and a motor drive the vehicle.
In the series hybrid vehicle, a power generating part using the internal combustion engine and a driving part using the motor can operate substantially separately. Therefore, the changeover between the operating state and the shutdown state of the internal combustion engine can be set freely. That is to say, the series hybrid vehicle can be set to any of: a mode in which the internal combustion engine is operated at all times, and a mode in which the internal combustion engine is intermittently driven (a mode in which changeover between the operating state and the shutdown state of the internal combustion engine is repeatedly performed).
In the case in which the vehicle is set to the mode in which the internal combustion engine is intermittently driven, the internal combustion engine is used as a range extender (RE) that extends a cruising range of the vehicle, and changeover is made between hybrid driving and EV driving (the internal combustion engine is shut down and driving by the motor is performed only by a battery), that is, the operating state and the shutdown state of the internal combustion engine is changed over, regardless of a driving state and a stopped state of the vehicle. Consequently, the time for shutting down the internal combustion engine temporarily may be longer (about several minutes) as compared to a so-called idling stopped vehicle.
Moreover, in the idling stopped vehicle, generally, in order to purify the exhaust gas at the time of restart of the internal combustion engine, a heater attached to the exhaust gas sensor is energized to activate the exhaust gas sensor during shutdown of the internal combustion engine.
In the exhaust gas sensor having the heater attached thereto, generally, after startup of the internal combustion engine, energization of the heater is performed after the exhaust gas temperature increases and it is determined that no condensed water is generated in the exhaust pipe, and there is no possibility of damage, such as cracking.
However, as in the range extender (RE) among the series hybrid vehicles, if temporary shutdown of the internal combustion engine (idling stop) continues for a long time after the internal combustion engine is activated and the exhaust gas temperature increases once, the temperature of the exhaust pipe decreases to generate condensed water. Then at the time of restart of the internal combustion engine, the condensed water splashes onto the exhaust gas sensor, and at that time, if energization of the heater is being performed, the probability of occurrence of cracking increases.
Moreover, in the series hybrid vehicle, when driving is performed while the internal combustion engine is shut down, the temperature of the exhaust pipe decreases due to the influence of the outside air temperature, the traveling wind, or heat dissipation, and there is a high probability of cracking of the exhaust gas sensor caused by water splashing.
An activation control apparatus of an air-fuel ratio sensor according to Japanese Laid-open Patent Application Publication No. H09-088688 considers that activation of the air-fuel ratio sensor is necessary at the time of shutdown of the engine due to engine automatic stop and start (eco-run), and energization control of a heater is implemented in order to hold the air-fuel ratio sensor in an activated state. That is to say, at the time of shutdown of the engine, a required time until the air-fuel ratio sensor becomes an inactivated state is estimated according to the temperature of engine cooling water, and when the required time has elapsed since shutdown of the engine, energization of the heater (duty control) is started. Moreover, energization of the heater is terminated at a point in time when a predetermined heater control termination time has elapsed since shutdown of the engine.
In a heater control apparatus of a sensor having a heater attached thereto according to Japanese Laid-open Patent Application Publication No. 2010-209799, in order to prevent cracking of the sensor caused by water splashing, energization of the heater is allowed when the exhaust gas temperature is equal to or higher than a first determination temperature, and also energization of the heater is allowed when the exhaust gas temperature is equal to or higher than a second determination temperature but is lower than the first determination temperature, and a degree of drying progress based on a history of exhaust gas temperature is equal to or higher than a predetermined determination value.